The present invention relates to systems and methods for inputting coordinate data to a host based on indicated coordinate positions.
Coordinate input systems for allowing operators to input given coordinates to hosts such as personal computers are known to date. In general, a coordinate input system samples coordinate positions continuously indicated with, for example, a coordinate input stylus at every given time and inputs sampled coordinate positions to a host as coordinate data. On the other hand, the host linearly interpolates the coordinate data so as to identify the path formed by coordinate positions indicated by an operator.
As the number of coordinate data units sampled as described above increases, the load necessary for arithmetic processing becomes heavier. In view of this, a conventional technique of omitting unnecessary coordinate data associated with an intermediate position so as to reduce the number of coordinate data units when the path formed by indicated coordinate positions is straight, for example, is known (see, for example, Japanese Unexamined Patent Publication No. 9-185454).
Specifically, a coordinate input system disclosed in Japanese Unexamined Patent Publication No. 9-185454 includes arithmetic means including: a coordinate data extracting section; a storage section, an angle deriving section; and an input section.
The coordinate data extracting section is configured to extract coordinate data at every given time from coordinate positions continuously indicated by an operator. The storage section stores the extracted coordinate data. The angle deriving section is configured to derive an angle which is the difference in direction between lines connecting points represented by the coordinate data to each other based on the stored coordinate data.
When the derived angle is smaller than a given value (e.g., when a coordinate input stylus, for example, indicating coordinate positions moves in a straight line), coordinate data associated with an intermediate position is discarded without being input to a host. On the other hand, when the derived angle is equal to or larger than the given value (e.g., the coordinate input stylus, for example, changes its direction and moves in a significantly different direction), coordinate data associated is input to the host. In this manner, the number of coordinate data units input to the host is reduced.
When an arithmetic circuit forming the arithmetic means is contaminated by a noise, there arises a problem in which coordinate data not agreeing with coordinate positions actually indicated by an operator is input to the host. However, in the coordinate input system disclosed in the above publication, redundant coordinate data is merely omitted when coordinate positions moves in a straight line. Therefore, the foregoing problem is not solved.
Regarding the foregoing problem, a coordinate input system including: an arithmetic circuit as described above; a display section including a back-light inverter; and an ultrasonic coordinate input stylus will be described as an example.
In the coordinate input system, an ultrasonic receiver for receiving an ultrasonic signal transmitted from the ultrasonic coordinate input stylus is provided. The ultrasonic receiver and the arithmetic circuit are connected to each other through a signal line.
This signal line might be contaminated by an ultrasonic noise generated from the back-light inverter. In this case, the ultrasonic noise causes abnormal coordinate data and this abnormal coordinate data is input to the host together with other normal coordinate data. As a result, the path formed by coordinate positions recognized by the host greatly deviates from the actual path indicated with the ultrasonic coordinate input stylus. That is, the noise contamination causes a problem in which desired coordinate data is not accurately input to the host.